A method for controlling an internal combustion engine is known from WO 97/35106. With the method, different estimated quantities such as the inlet pipe pressure, the mass flow rate in the air intake tract in the area of the throttle valve, the mass flow rate into the cylinders of the internal combustion engine and the exhaust gas back-pressure are determined by means of an observer. An observer can determine estimated values of certain quantities, i.e. estimated quantities, of a system, in this case the internal combustion engine, in each case as a function of recorded measured variables or further estimated values. This is achieved through appropriate modeling of the system of the internal combustion engine. Thus, more quantities can be used to control the internal combustion engine than are recorded by sensors. With regard to low exhaust gas emissions of the internal combustion engine it is necessary to determine all the quantities with great precision—thus also the estimated quantities.